Question

1. The table below shows the percentage of the body composed of water for various vertebrates. Animal % of body composed of water Herring Frog Chicken Kangaroo 67 78 74 65 Rat Which animal would you expect to have the most concentrated urine? Provide a reason for your prediction. The kangaroo rat and the chicken feed largely on plant products, while the herring and frog are carnivores. Explain how food source would affect urine composition. Why would the concentration of urea be higher in the kangaroo rat than in the herring? 2. Compare how peptide and steroid hormones affect their target cells.

Please help me solve the following 2 questions

Answer 1

Answer 1 (a) Kangaroo rat is expected to have most concentrated urine because, among all the animals mentioned above, kangaroo rat has the least composition of water in its body (65%). So, in order to preserve water in its body, it must excrete urine with less water (or concentrated urine).

Answer 1 (b) Urea composition in kangaroo rat and chicken (herbivores) would be different than in herring and frog (carnivore) due to their differences in dietary sources. Ist difference would be in their urine pH. Herbivores generally have alkaline (pH>7) urine while carnivores have acidic (pH<7) urine. Second difference would be the concentration- kangaroo rat and chicken's urine would be highly concentrated in the form of uric acid crystals while the urine of herring and frog would be less concentrated and mainly composed of urea.

Answer 1 (c) The concentration of urea would be higher in kangaroo rat than in herring because the former excrete very thick urine in order to preserve water in extremely dry temperature of desserts. They also need urea in order to main the osmolarity of the body fluids. That is why they preserve urea while herring excrete it in its urine.

Answer 2. Peptide hormones (e.g. Insulin, glucagon, Growth hormone etc.) are generally hydrophilic and unable to pass to the plasma membrane, therefore, they bind their receptors on the cell surface such as G-protein coupled receptor (GPCR).

Steroid hormones (e,g, testosterone, estrogen, cortisol etc.) are hydrophobic and can easily pass through the plasma membrane through diffusion and then bind to the intracellular receptors (nuclear family receptors)